Semiconductor devices are used in a large number of electronic devices, such as computers, cell phones, and others. Semiconductor devices comprise integrated circuits that are formed on semiconductor wafers by depositing many types of thin films of material over the semiconductor wafers, and patterning the thin films of material to form the integrated circuits. Integrated circuits include field-effect transistors (FETs) such as metal oxide semiconductor (MOS) transistors.
One of the goals of the semiconductor industry is to continue shrinking the size and increasing the speed of individual FETs. To achieve these goals, fin FETs (FinFETs) or multiple gate transistors will be used in sub 32 nm transistor nodes. For example, FinFETs not only improve areal density but also improve gate control of the channel.
In constructing three-dimensional FinFETs, an epitaxially grown layer of semiconductor material (“epi layer”) is generally grown on a semiconductor substrate. Because the thickness of the epi layer (i.e., the height that the epi layer rises above the semiconductor substrate) affects the performance of the FinFET, growth of the epi layer is, if possible, precisely controlled.
The rate at which an epi layer grows in or proximate different environments (e.g., on silicon, adjacent to a shallow trench isolation (STI) region, proximate a silicon nitride, etc.) varies significantly. In order to determine if an epi layer has grown to an expected, desired, or acceptable thickness, a transmission electron microscope (TEM) may be used and thickness measurements taken. However, using the TEM is costly. Therefore, using the TEM sparingly may be desired. In addition, using the TEM to take measurements may slow down the overall FinFET production process. Moreover, the TEM is unable to observe variations within the die without taking an extensive number of measurements.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.